1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, particularly a projector for projecting light modulated through a liquid crystal panel on a screen.
2. Description of the Related Art
Heretofore, projectors have been used for extended projection of presentation materials for conferences and lectures. These projectors have been provided with higher luminance because of their uses under bright indoor conditions, unlike those for family use.
Such projector set with higher luminance is regarded as a higher-end model and the higher contrast thereof can be thus desired. In recent years, it is also important to reduce the costs of projectors as the projectors have become popular.
Such a projector forms an image by separating light from a light source into three different colors, red, green, and blue, through a wavelength-selectable filter and combining these red, green, and blue rays by a color-composition prism after passing through respective light modulation devices.
The light modulation device employs a liquid crystal panel. The well-known liquid crystal panel may be a twist nematic (TN) liquid crystal panel. In the TN liquid crystal panel, liquid crystal molecules are twisted in helical form in the direction parallel to a glass substrate without an applied voltage. The TN liquid crystal panel is configured such that light incident thereon can turn 90 degrees and pass therethrough (so-called “normally white”). Liquid crystal molecules stand up perpendicularly to the glass substrate when a voltage is applied, so that the transmission of light can be prevented. In the TN liquid crystal panel, the liquid crystals adjacent to the glass substrate may not completely stand up and are left inclined. Thus, light will be leaked at the time of black representation, leading to a decrease in contrast.
A vertically aligned (VA) liquid crystal panel is configured in contrast with the above configuration of the TN liquid crystal panel. In the VA liquid crystal panel, liquid crystal molecules stand up perpendicularly to the glass substrate without voltage application, resulting in normally black representation. When a voltage is applied, the liquid crystal molecule is inclined in parallel with the glass substrate and twisted to allow the transmission of light. With the VA liquid crystal panel configured as described above, such light leakage from the panel that occurs in the TN liquid crystal panel may not be caused at the time of black representation. Thus, the VA liquid crystal can attain higher contrast than that of the TN liquid crystal panel.
The costs of projectors have been decreased, and the liquid crystal panels also tend to be small-sized. In addition, the projector is provided with an incidence-side polarizer and an output-side polarizer in a crossed nicol state. Here, the incidence-side polarizer is provided for aligning the polarized state of light incident on the liquid crystal panel and the output-side polarizer is provided for the selective transmission of light output from the liquid crystal panel.
The polarizers, which have been typically used in the art, may be those in which a film formed by drawing out an organic dye material is attached on a base material (organic polarizer). Sapphire or other base material with high thermal conductivity is also used for such an organic polarizer with the projectors having been provided with higher luminance in recent years.
The polarizer having a structure different from the organic polarizer may be a reflective inorganic polarizer, such as a wire-grid (WG) polarizer, or an absorptive inorganic polarizer. These polarizers are also known in the art (see, for example, Japanese Unexamined Patent Application Publication No. 2006-323119) and have been commercially available.
Japanese Unexamined Patent Application Publication No. H10-133196 (Paragraph Nos. 0005 to 0008 and 0018 to 0020) proposes a technology that, with an organic polarizer being used, intends to reduce the thermal load on the polarizer by providing at least one of the incidence-side polarizer and the output-side polarizer to include a plurality of polarizers.
Further, for realizing a high contrast, a technology for providing a mechanism for turning an organic polarizer on the incidence side around an optical axis and a technology for arranging an optical compensator on the incidence-side or output-side of a liquid crystal panel have been also known in the art (Japanese Unexamined Patent Application Publication No. 2005-107364 Paragraph Nos. 0027, 0034, and 0038).